[Apoptosis in MDS].

We examined the endonuclease activity capable of inducing internucleosomal DNA fragmentation in hematopoietic cells. Mg(2+)-dependent nuclease activity was high in hematopoietic progenitor cells and the activity decreased with myeloid or erythroid differentiation. This was the case in MDS as well as in normal hematopoiesis. In contrast, Ca2+/Mg(2+)-dependent nuclease activity varied widely in the samples from MDS and the possibility was indicated that the activity of Glycophorin A+ cells was related to the degree of anemia. We also investigated DNA strand breaks in bone marrow samples from 16 patients with MDS and 10 with other diseases by an in situ end labeling (ISEL) technique. The reactivity in ISEL tended to increase parallel to disease progression of MDS. The high ISEL-positivity was also observed in some samples from patients with MPD and other diseases. Though ISEL is a useful technique for quantification of apoptosis, our results suggested that MDS cells with ISEL positive staining are not necessarily in the process of apoptosis.